Is the new Alpha Go implementation using Generative Adversarial Networks?
No, GANs are not used. It's reinforcement learning at what it does best. The tree search is an interesting addition and assists with navigating the sheer scale of the game. 

Although the agent was playing itself to become better, there wasn't 2 separate networks (generator and discriminator). The agent learned through RL and didn't have the error calculations that generators and discriminatory have.